fix(release): support Ubuntu 22.04 protoc

[ovasylenko]

Summary

• pass the proto3 optional compatibility flag required by Ubuntu 22.04's protoc 3.12
• bump the replacement release candidate to v0.7.0-rc.3 and refresh lockfiles/docs
• guard the required protobuf option in release regression tests

Root cause

v0.7.0-rc.2 fixed GNU glibc compatibility by building on Ubuntu 22.04, but that runner's protoc rejected proto3 optional fields without the compatibility flag. The failed candidate produced no GitHub Release or container manifest, and its mobile publication run was cancelled.

Validation

• cargo fmt --all -- --check
• cargo metadata --locked --format-version 1
• cargo metadata --locked --offline --manifest-path fuzz/Cargo.toml --format-version 1
• bash scripts/test-review-fix-guards.sh
• cargo test -p orch8-grpc (254 passed)